FIG. 1 is a block diagram of a network structure of a universal mobile telecommunications system (UMTS). Referring to FIG. 1, a UMTS mainly includes a user equipment (UE), a UMTS terrestrial radio access network (UTRAN), and a core network (CN).
The UTRAN includes at least one radio network sub-system (hereinafter abbreviated RNS). The RNS includes one radio network controller (RNC) and at least one base station (Node B) managed by the RNC. At least one or more cells exist in one Node B.
FIG. 2 is an architectural diagram of a radio interface protocol between the UE (user equipment) and the UTRAN (UMTS terrestrial radio access network). Referring to FIG. 2, a radio interface protocol vertically includes a physical layer, a data link layer, and a network layer. Horizontally, the radio interface protocol includes a user plane for data information transfer and a control plane for signaling transfer.
The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) such as the three lower layers of an open system interconnection (OSI) standard model widely known in the art. The respective layers in FIG. 2 are explained as follows.
A physical layer (PHY) is the first layer and offers an information transfer service to an upper layer using a physical channel. The physical layer (PHY) is connected to a medium access control (MAC) layer located above the physical layer PHY via a transport channel. Data is transferred between the MAC layer and the PHY layer via the transport channel. Moreover, data is transferred between different physical layers, and more particularly, between a physical layer of a transmitting side and a physical layer of a receiving side via the physical channel.
The MAC layer of the second layer offers a service to a radio link control (RLC) layer located above the MAC layer via a logical channel. The MAC layer can also be divided into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, a MAC-hs sublayer and a MAC-e sublayer according to the types of transport channels managed in detail.
The MAC-b sublayer takes charge of managing a transport channel such as a broadcast channel (BCH) responsible for broadcasting system information. The MAC-c/sh sublayer manages a shared transport channel, which is shared by other UEs. A forward access channel (FACH) and a downlink shared channel (DSCH) are examples of a shared transport channel. The MAC-d sublayer takes charge of managing a dedicated transport channel such as a DCH (dedicated channel) for a specific UE. The MAC-hs sublayer manages a transport channel such as a high speed downlink shared channel (HS-DSCH) for supporting high speed data transfer in downlink and uplink. The MAC-e sublayer manages a transport channel such as an enhanced dedicated channel (E-DCH) for uplink data transfer.
FIG. 3 is a diagram of a structural example of DCH and E-DCH. Referring to FIG. 3, both DCH and E-DCH are transport channels that can be dedicatedly used by one user equipment (UE). In particular, the E-DCH is used by a user equipment to transfer data to a UTRAN in uplink. Compared to the DCH, the E-DCH can transfer uplink data faster than the DCH. To transfer data at high speed, the E-DCH adopts a technique such as hybrid automatic repeat request (HARQ), adaptive modulation and coding (AMC) and scheduling controlled by a Node B, for example.
For E-DCH, the Node B transfers to the UE downlink control information for controlling the UE's E-DCH transfer. The downlink control information includes response information (ACK/NACK) for HARQ, channel quality information for AMC, E-DCH transport rate assignment information, E-DCH transport start time and transport time interval assignment information, and transport block size information, for example. Meanwhile, the UE transfers uplink control information to the Node B. The uplink control information includes E-DCH rate request information for Node B controlled scheduling, UE buffer status information, and UE power status information, for example. The uplink and downlink control information for E-DCH is transferred via a physical control channel such as an enhanced dedicated physical control channel (E-DPCCH).
A MAC-d flow is defined between a MAC-d sublayer and a MAC-e sublayer for E-DCH. In this case, a dedicated logical channel is mapped to the MAC-d flow. The MAC-d flow is mapped to a transport channel E-DCH, and the E-DCH is mapped to another physical channel E-DPDCH (enhanced dedicated physical data channel). On the other hand, the dedicated logical channel can be directly mapped to DCH. In this case, the transport channel DCH is mapped to a dedicated physical data channel (DPDCH). The MAC-d sublayer in FIG. 3 manages the DCH (dedicated channel) as a dedicated transport channel for a specific user equipment, while the MAC-e sublayer manages the E-DCH (enhanced dedicated channel) as a transport channel used in transferring fast data in uplink.
A MAC-d sublayer of a transmitting side configures a MAC-d protocol data unit (PDU) from a MAC-d service data unit (SDU) delivered from an upper layer, i.e., an RLC layer. A MAC-d sublayer of a receiving side facilitates recovery of the MAC-d SDU from the MAC-d PDU received from a lower layer and delivers the recovered MAC-d SDU to an upper layer. In doing so, the MAC-d exchanges the MAC-d PDU with a MAC-e sublayer via a MAC-d flow or exchanges the MAC-d PDU with a physical layer via the DCH. The MAC-d sublayer of the receiving side recovers the MAC-d PDU using a MAC-d header attached to the MAC-d PDU prior to delivering the recovered MAC-d SDU to an upper layer.
A MAC-e sublayer of a transmitting side configures a MAC-e PDU from a MAC-e SDU corresponding to a MAC-d PDU delivered from an upper layer, i.e., a MAC-d sublayer. The MAC-e sublayer of a receiving side facilitates recovery of the MAC-e SDU from the MAC-e PDU received from a lower layer, i.e., a physical layer and delivers the recovered MAC-e SDU to a higher layer. In doing so, the MAC-e exchanges the MAC-e PDU with the physical layer via the E-DCH. The MAC-e sublayer of the receiving side recovers the MAC-e SDU using a MAC-e header attached to the MAC-e PDU prior to delivering the recovered MAC-e SDU to a higher layer.
FIG. 4 is a diagram of a protocol for E-DCH. Referring to FIG. 4, a MAC-e sublayer supporting E-DCH exists below a MAC-d sublayer of a UTRAN. Furthermore, a MAC-e sublayer supporting E-DCH exists below a MAC-d sublayer of a UE. The MAC-e sublayer of the UTRAN is located at a Node B. The MAC-e sublayer exists in each UE. On the other hand, the MAC-d sublayer of the UTRAN is located at a serving radio network controller (SRNC) in charge of managing a corresponding UE. The MAC-d sublayer exists in each UE.
Control information transmission for E-DCH is explained as follows. First of all, a scheduler exists at a Node B for E-DCH. The scheduler facilitates the allocation of an optimal radio resource to each UE existing within one cell to raise transmission efficiency of data in an uplink transfer at a base station from all UEs within each cell. In particular, more radio resources are allocated to a UE having a good channel status in one cell to enable the corresponding UE to transmit more data. Less radio resources are allocated to a UE having a poor channel status to prevent the corresponding UE from transmitting interference signals over an uplink radio channel.
When allocating radio resources to the corresponding UE, the scheduler does not only consider a radio channel status of a UE. The scheduler also requires control information from UEs. For example, the control information includes a power quantity the UE can use for E-DCH or a quantity of data the UE attempts to transmit. Namely, even if the UE has a better channel status, if there is no spare power the UE can use for E-DCH, or if there is no data the UE will transmit in an uplink direction, a radio resource should not be allocated to the UE. In other words, the scheduler can raise the efficiency of radio resource use within one cell only if a radio resource is allocated to a UE having a spare power for E-DCH and data to be transmitted in the uplink transfer.
Accordingly, a UE should send control information to a scheduler of a Node B. The control information can be transmitted in various ways. For instance, a scheduler of a Node B can instruct a UE to report that data to be transmitted in uplink exceeds a specific value or to periodically send control information to the Node B itself.
In case a radio resource is allocated to a UE from a scheduler of a Node B, the UE configures a MAC-e PDU within the allocated radio resource and then transmits the MAC-e PDU to a base station via E-DCH. In particular, if there exists data to be transmitted, a UE sends control information to a Node B to inform the Node-b that there is data to be transmitted by the UE. A scheduler of the Node B then sends information indicating that a radio resource allocation will be made to the UE based on the control information been sent by the UE. In this case, the information indicating the radio resource allocation means a maximum value of power the UE can transmit in uplink, a ratio for a reference channel, etc. The UE configures the MAC-e PDU within a permitted range based on the information indicating the radio resource allocation and transmits the configured MAC-e PDU.
However, in the related art method, a UE transmits a MAC-e PDU, which starts a transmission, until receiving an acknowledgement (ACK) from the Node B that the MAC-e PDU was correctly received by the Node B, or retransmits the MAC-e PDU as many times as a maximum retransmission attempt value allows. Accordingly, when new data arrives at the UE to be transmitted to the Node B, new control information should also be transmitted to the Node B to request a resource allocation for the new data transmission. However, in the related art as shown in FIG. 5, the UE must wait until receiving an ACK from the Node B or retransmit an old MAC-e PDU a maximum number of times allowable before transmitting a new or updated MAC-e PDU with the new control information. Accordingly, a time taken for a UE to receive a radio resource allocation is delayed. Furthermore, by considering that information such as power information is frequently changed, wrong or old information is delivered to a Node B under the related art method.